An Intercalibrated Microwave Radiance Product for Use in Rainfall Estimation Level 1C Christian Kummerow, Wes Berg, G. Elsaesser Dept. of Atmospheric Science Colorado State University 3rd IPWG Workshop Melbourne, Australia Oct , 2006

Original Motivation GPM will fly a constellation of radiometers to provide ~3-hourly sampling. If the radiometers are not inter-calibrated, neither will the rain rates. Except for the dedicated GPM radiometers (GMI), the remaining set belongs to US and International agencies that have differing experience and requirements for calibration. These agencies may or may not support calibration activities once their own requirements are met. Level 1C is an attempt to overcome political and programmatic issues and return “calibration” and data stewardship to the rainfall community Level 1C aims to simplify formats and toolkits. “If a graduate student knows how to read data from one sensor, they can read it from all sensors”

TMI * º AMSR-E º SSM/I * º SSMIS * ** /-1, 3, 7**53.1º WINDSAT *** 18.7*** ***49.9º- 55.3º Sensor Inc Ang Chan Freq (GHz) *V-Pol only **H-Pol only ***V, H, +/45º, L, R Today’s GPM constellation

AMSR-E Calibration Differences

Effect of SSM/I Calibration on rainfall

Inter-calibration Procedure  Select coincident overpasses (±30 min.) of TMI and SSM/I (other sensors will be done in same fashion but waiting for next version of algorithm below)  Use current retrieval method (OE in non-raining + PR adjustment in rain) to derive geophysical parameter field that is consistent with each TMI Tb  Use geophysical parameters to compute Tb for each SSM/I sensor using appropriate channels, view angles and spatial resolution  Compute biases in computed SSM/I Tb versus observed Tb.  Use as much data as possible to reduce random errors.

SSM/I – TMI Crossover

TMI Simulated Simulated TBs vs Observed TBs 19 H (K)21 V (K) 37 H (K) 85 V (K) TMI Simulated

SSM/I Calibration

SSM/I Calibration Offsets Sat19V19H22V37V37H85V85H F F F F

TMI SSM/I F13 SSM/I F14 AMSR-E SSM/I F15 19 H 19 V 22 V 37 H 37 V 86 H 86 V TB Bias (Simulated Minus Observed) in Kelvins Approximate Channel Frequency Level 1C Calibration Differences

Level 1C Project

 Pixel check for nonphysical values: Checks that individual antenna temperatures values are within physical limits (currently 50 to 325K), that lat/lon values are within range (-90 to 90 and -180 to 360), and that the distance between pixels along a scan are reasonable (10 to 30km).  Scan check for nonphysical seperation: Checks that the distance between adjacent scans (nadir point) is between 20 and 30 km. Scans outside of this range are flagged and are currently eliminated (not written out).  Scan check for deviations from climatology: Compares the antenna temperatures for each channel along the scan to climatological values. If more than 30% of the pixels along a given scan are greater outside the range of the mean climatological TA +/- 3 sigma, and this represents a change of 30% or more from the prior scan, the scan is flagged and eliminated (not written out). Level 1C development Quality Control Procedures

Level 1C Data Availability

Naming Convention F11.1C.CALT1.R HDF T : TMI was used as reference standard 1 : Maturity level 0: Nothing has been done to calibrate the Tb to the reference sensor 1: Data has been re-calibrated to match the reference instrument 2: The intercalibration has been verified by at least one independent effort 3: The intercalibration has been accepted by the Precipitation Science Team R : Revision number 1 : Initial Version R2, R3 etc.) indicate substantive changes to the data, data format, and/or file contents, which imply reprocessing of the entire data record. Minor revisions to the files, such as might occur with a change to the metadata, are indicated by a lower case letter following the revision number (i.e. 1a, 1b, etc.).

Available Rainfall Maps